1. Field of the Invention
The present invention generally relates to a semiconductor device. More particularly, the present invention relates to a semiconductor device that prevents copper of copper wiring from diffusing into a memory storage portion for storing information.
2. Description of the Background Art
With ever-increasing demand to shrink the semiconductor devices in dimensions, the wiring width: has been reduced. Moreover, a wiring material has increasingly changed from aluminum wiring to copper wiring in order to reduce the electrical resistance and also the wiring width. The copper wiring has a reduced wiring width mainly because of the damascene method. Replacing aluminum wiring with copper wiring has the following benefits:
(a) Electrical resistance of the wiring can be reduced, so that the wiring delay time is reduced, and an operation frequency can be increased, resulting in an increased operating speed of the semiconductor device. Reduction in electrical resistance also results in reduced capacity between adjacent wires, whereby the wiring delay time can further be reduced;
(b) Reduction in electrical resistance results in reduced power consumption, and also enables the amount of heat generation to be reduced even with a higher integration degree; and
(c) The copper wiring is, normally formed according to the damascene method, so that the copper wiring width can be reduced, resulting in a dimensionally shrunk semiconductor device.
However, copper atoms have a property of easily diffusing into silicon and a silicon oxide film. Therefore, a copper bridge is formed between copper wires, causing short-circuit thereof. Moreover, the copper atoms get into an active region of the silicon substrate, resulting in unsatisfactory characteristics and malfunctioning.
Accordingly, some proposals have been made in order to prevent characteristics of the semiconductor device from being degraded by diffusion of copper atoms from copper wiring through silicon into an active region or the like. For example, the following proposal has been made in order to prevent copper diffusion from a copper-film wiring pattern into an active region of the semiconductor substrate: more specifically, a proposal has been made to form an amorphous barrier film on top and bottom of a copper wiring pattern formed in an upper layer (Japanese Patent Laying-Open No. 10-256256). According to this method, copper does not diffuse from the top and bottom surfaces of the copper film. In addition, the following proposal has been made in order to prevent copper diffusion from a copper wiring layer into a silicon substrate: first, a copper-diffusion barrier film is formed, on the sidewall of a contact hole formed in an interlayer insulating layer and on the bottom and sidewall of a patterned wiring groove in the interlayer insulating layer. Then, a metallic compound mainly comprised of copper is embedded thereon, so that an embedded wiring layer is formed (Japanese Patent Laying-Open No. 10-98011). According to this method, copper does not diffuse downward from the embedded copper wiring layer, and therefore characteristics of an underlying active layer are not degraded. Moreover, the following proposal has been made in order to prevent copper atoms from diffusing from copper wiring into a silicon substrate and oxide film: a copper-diffusion barrier film is formed on the bottom and sidewall of a wiring groove formed in an interlayer insulating film. Then, a,copper film is formed thereon and heated for reflow, so that the copper film is embedded in the wiring groove (Japanese Patent Laying-Open No. 8-148560). This method also prevents the copper atoms from diffusing from the copper film, the wiring layer, into an underlying active region.
However, with the progress in dimensional shrinking of the semiconductor devices, a problematic amount of copper has become far smaller than that is conventionally problematic. More specifically, as shown in FIG. 22, in the case where the copper wiring is used in, e.g., a DRAM (Dynamic Random Access Memory), copper atoms get into capacitors of a memory cell portion in the DRAM, destroying charges corresponding to information. A capacitor has a dielectric film interposed between electrodes, and stores 1-bit information according to presence/absence of accumulated charges in the electrodes. The copper atoms getting into the capacitor cause dissipation of charges within the dielectric, destroying an information storage function. In FIG. 22, a wiring portion 150 is provided over a memory cell portion 130 and a peripheral circuit portion 140, and copper wires 116a and 116b for connecting the corresponding contacts are provided in the wiring portion 150. The copper wires 116a and 116b in the peripheral circuit portion are connected through corresponding contacts 109c and 113c to corresponding source/drain regions 106 formed with a respective gate electrode 104 interposed therebetween. Gate electrodes 104 are arranged in the memory cell portion 130, and a lift pad 108 extends from each active region located between the gate electrodes 104. A capacitor contact 111 is formed on the lift pad 108, and a capacitor 112 comprised of a lower electrode 112a, a dielectric 112b and an upper electrode 112c is connected thereto. When this semiconductor device is subjected to heat during the manufacturing process, copper atoms diffuse from the copper film into the capacitors in the memory cell portion 130. Moreover, while the finished semiconductor device is in use, the copper atoms move into the capacitors due to electrodiffusion. The capacitors are destroyed even when the above-mentioned conventional measures are taken to prevent copper diffusion. Accordingly, the problematic amount of copper herein is far smaller than the conventionally problematic amount. Therefore, in the field of semiconductor devices, development of semiconductor devices sustaining a stable memory cell operation for a long time while still having the above-mentioned benefits of copper wiring has been strongly demanded.
It is an object of the present invention to provide a semiconductor device capable of reliably preventing diffusion of copper atoms even in a slight amount, and also capable of easily forming means for preventing the copper diffusion.
The semiconductor device of the present invention has a memory storage portion and a wiring portion including a copper wire apart from the memory storage portion on a semiconductor substrate. The semiconductor device includes copper diffusion blocking means provided in a region surrounding the memory storage portion for blocking copper diffusion from the wiring portion toward the memory storage portion.
The region surrounding the memory storage region is located away from the copper wire. Therefore, in this region, the driving force for diffusion of copper atoms is small. Since the copper-diffusion blocking means is provided in this region, diffusion of copper atoms can be reliably prevented even in a slight amount. Moreover, the copper-diffusion blocking means provided in this region allows for a simple structure that is easy to produce. Therefore, with the copper-diffusion blocking means having a simple shape, diffusion of copper atoms into the memory storage portion that destroys information therein can be prevented while still enjoying the benefits of copper wiring.
The memory storage portion as used herein mainly indicates a memory storage portion of the type that stores information corresponding to presence/absence of charges. However, the present invention is not limited to this. Semiconductor devices for storing information corresponding to presence/absence of charges include a DRAM (Dynamic Random Access Memory), EPROM (Erasable Programmable Read Only Memory) including a flash memory, EEPROM (Electrically Erasable Programmable Read Only Memory), and charge-transfer sequential access memory. When copper gets into the memory storage portion of this type, the amount of accumulated charges therein is significantly varied. In other words, such semiconductor devices are highly sensitive to copper as impurities. Semiconductor devices having the highest copper sensitivity include a DRAM for storing information corresponding accumulated charges in a capacitor. The DRAM stores 1-bit information according to presence/absence of accumulated charges in a capacitor provided for each transistor. More specifically, in the DRAM, capacitors in a memory cell portion, i.e., in the memory storage portion, share the information storage function. Therefore, copper diffusion into the memory cell portion causes malfunctioning of the DRAM, so that the DRAM no longer functions as DRAM. Copper wiring using the damascene method is effective in dimensionally shrinking the devices. However, as the devices are increasingly shrunk, the distance between a copper wire and memory cell portion is reduced, whereby the copper atoms are more likely to diffuse into the memory cell portion. Therefore, in the case where the copper wiring that is effective for shrinking is used in a semiconductor device having memory cells including capacitors, provision of the copper-diffusion blocking means is very important.
Note that the barrier layer mentioned in background of the invention is desirably formed on the copper wire. The term xe2x80x9cdiffusionxe2x80x9d as used herein refers to almost all the copper-moving phenomena including movement due to thermal diffusion and electrodiffusion. The copper diffusion as used herein includes diffusion of copper atoms and diffusion of copper ions. Herein, copper atoms and copper ions are not specifically distinguished, and are simply referred to as copper atoms or copper.
In the semiconductor device of the present invention, the region surrounding the memory storage portion includes, for example, a top-surface region and a side-surface region of the memory storage portion, and the copper-diffusion blocking means can be located in at least one of the top-surface region and the side-surface region.
The top-surface region: of the memory storage portion refers to a region that is opposite to the semiconductor substrate with the memory storage portion therebetween and that overlaps the memory storage portion as viewed two-dimensionally The side-surface region of the memory storage portion refers to a vertical-wall region that extend to cross the semiconductor substrate and that surrounds the memory storage portion as viewed two-dimensionally. The top-surface region and the side-surface region are in contact with each other, and located in a region between the memory storage portion and the wiring portion. According to the above-mentioned structure, every part of the wiring portion cannot linearly lead to any part of the memory storage portion without passing through at least one of the top-surface region and side-surface region. By providing the copper-diffusion blocking means in at least one of the top-surface region and the side-surface region, the amount of copper diffusing from the copper wire into the memory storage portion is reduced, whereby destruction of the memory is suppressed. The copper-diffusion blocking means may be located across the whole region of at least one of the top-surface region and the side-surface region, or may be located in a part of at least one of the top-surface region and the side-surface region.
In the semiconductor device of the present invention, copper-diffusion blocking means that is provided in the top-surface region out of the copper-diffusion blocking means is desirably located across the whole top-surface region.
With such a structure, copper atoms are reliably prevented from diffusing through the top-surface region into the memory storage portion. As a result, destruction of the information storage function of the memory is significantly suppressed.
In the semiconductor device of the present invention, copper-diffusion blocking means that is provided in the side-surface region out of the copper-diffusion blocking means is desirably located across the whole side-surface region.
With such a structure, copper atoms are reliably prevented from diffusing through the side-surface region into the memory storage portion. As a result, destruction of the information storage function of the memory is significantly suppressed. In the present invention, copper-diffusion blocking means may be provided so as to cover whole range of the region surrounding the memory storage portion or may be provided so as to occupy a part of the region, as far as it blocks copper diffusion to the memory storage portion.
In the semiconductor device of the present invention, the region surrounding the memory storage portion includes a top-surface region and a side-surface region of the memory storage portion, and the copper-diffusion blocking means can be located, for example, across a whole region of both the top-surface region and the side-surface region.
By providing the copper-diffusion blocking means across the whole region of both the top-surface, region and side-surface region, copper diffusion from the wiring portion into the memory storage portion can be reliably prevented, so that even a slight amount of copper does not diffuse into the memory storage portion. More specifically, copper is prevented from diffusing into the memory storage portion even in a slight amount due to thermal diffusion during manufacturing of the semiconductor device and electrodiffusion during use thereof. As a result, a reliable semiconductor device operating stably for a long time while still having the benefits of copper wiring can be provided.
In the semiconductor device of the present invention, the copper-diffusion blocking means is, for example, a copper-diffusion preventing film.
In this case, the copper-diffusion preventing film can be easily formed during manufacturing process of the semiconductor device by using normal thin-film formation technology. This copper-diffusion preventing film may be formed in parallel with the semiconductor substrate. Alternatively, the copper-diffusion preventing film may be formed as a vertical wall embedded in a trench formed in an insulating film at an angle to the semiconductor substrate.
In the semiconductor device of the present invention, the top-surface region desirably includes an insulating film located over the memory storage portion, and the copper-diffusion preventing film is desirably located in the insulating film so as to extend in parallel with a surface of the semiconductor substrate.
Since the insulating film is interposed between the memory storage portion and the copper-diffusion preventing film in the top-surface region, a material forming the copper-diffusion preventing film is not limited to an insulating material, and a metal film may be used.
In the semiconductor device of the present invention, the side-surface region desirably includes an insulating film surrounding the memory storage portion, and the copper-diffusion preventing film is desirably formed like a vertical wall in the insulating film so as to cross a surface of the semiconductor substrate.
The copper-diffusion preventing film in the side-surface region can also be formed from any material, since the insulating film is interposed between the memory storage portion and the copper-diffusion preventing film. As described above, the vertical-wall-like copper-diffusion preventing film can be easily formed by embedding the copper-diffusion preventing film in a trench formed in the insulating film.
In the semiconductor device of the present invention, the memory storage portion may be, for example, a memory storage portion for accumulating and releasing charges according to information.
The memory storage portion for accumulating and releasing charges according to information includes a memory cell portion of the DRAM. The DRAM accumulates and releases the charges in and from capacitors so as to store 1-bit information per capacitor. These capacitors are highly conveniently formed at a high density. By providing the copper-diffusion preventing film, the conveniently formed high-density capacitors can be used as memory cells in a dimensionally shrunk semiconductor device having the benefits of copper wiring. Moreover, since a flash memory such as EPROM and EEPROM also accumulates and releases charges to store information according to presence/absence of the charges, the same effects as those of the DRAM can be obtained.
In the semiconductor device of the present invention, each copper-diffusion preventing film forming the copper-diffusion blocking means may be, for example, any one of a tungsten film, an aluminum film, a silicon nitride film, a tantalum film and a tantalum nitride film.
These films can reliably block diffusion of copper atoms, and have been actually formed in the manufacturing process of the semiconductor devices. Therefore, in the manufacturing process of the semiconductor device of the present invention, a film capable of reliably preventing copper diffusion can be formed without significant modification such as remodeling of an apparatus for manufacturing the semiconductor device, and thus without significant increase in cost.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.